Mechanisms of tubulo-interstitial injury in progressive renal diseases

New Insights Into the Role and Mechanism of Partial Epithelial-Mesenchymal Transition in Kidney Fibrosis

Epithelial-mesenchymal transition (EMT) is described as the process in which injured renal tubular epithelial cells undergo a phenotype change, acquiring mesenchymal characteristics and morphing into fibroblasts. Initially, it was widely thought of as a critical mechanism of fibrogenesis underlying chronic kidney disease. However, evidence that renal tubular epithelial cells can cross the basement membrane and become fibroblasts in the renal interstitium is rare, leading to debate about the existence of EMT. Recent research has demonstrated that after injury, renal tubular epithelial cells acquire mesenchymal characteristics and the ability to produce a variety of profibrotic factors and cytokines, but remain attached to the basement membrane. On this basis, a new concept of “partial epithelial-mesenchymal transition (pEMT)” was proposed to explain the contribution of renal epithelial cells to renal fibrogenesis. In this review, we discuss the concept of pEMT and the most recent findings related to this process, including cell cycle arrest, metabolic alternation of epithelial cells, infiltration of immune cells, epigenetic regulation as well as the novel signaling pathways that mediate this disturbed epithelial-mesenchymal communication. A deeper understanding of the role and the mechanism of pEMT may help in developing novel therapies to prevent and halt fibrosis in kidney disease.

Renal oxygenation during the early stages of adenine-induced chronic kidney disease

To assess whether renal hypoxia is an early event in adenine-induced chronic kidney disease, adenine (100 mg) or its vehicle was administered to male Sprague-Dawley rats by daily oral gavage for 7 days. Kidney oxygenation was assessed by 1) blood oximetry and Clark electrode in thiobutabarbital-anesthetized rats, 2) radiotelemetry in unanesthetized rats, and 3) expression of hypoxia-inducible factor (HIF)-1α and HIF-2α protein. After 7 days of treatment, under anesthesia, renal O2 delivery was 51% less, whereas renal O2 consumption was 65% less, in adenine-treated rats than in vehicle-treated rats. Tissue Po2 measured by Clark electrode was similar in the renal cortex but 44% less in the medulla of adenine-treated rats than in that of vehicle-treated rats. In contrast, in unanesthetized rats, both cortical and medullary tissue Po2 measured by radiotelemetry remained stable across 7 days of adenine treatment. Notably, anesthesia and laparotomy led to greater reductions in medullary tissue Po2 measured by radiotelemetry in rats treated with adenine (37%) than in vehicle-treated rats (16%), possibly explaining differences between our observations with Clark electrodes and radiotelemetry. Renal expression of HIF-1α was less after 7 days of adenine treatment than after vehicle treatment, whereas expression of HIF-2α did not differ significantly between the two groups. Renal dysfunction was evident after 7 days of adenine treatment, with glomerular filtration rate 65% less and serum creatinine concentration 183% greater in adenine-treated rats than in vehicle-treated rats. Renal cortical tissue hypoxia may not precede renal dysfunction in adenine-induced chronic kidney disease and so may not be an early pathological feature in this model.

The Key Role of Epithelial to Mesenchymal Transition (EMT) in Hypertensive Kidney Disease

Accumulating evidence indicates that epithelial-to-mesenchymal transition (EMT), originally described as a key process for organ development and metastasis budding in cancer, plays a key role in the development of renal fibrosis in several diseases, including hypertensive nephroangiosclerosis. We herein reviewed the concept of EMT and its role in renal diseases, with particular focus on hypertensive kidney disease, the second leading cause of end-stage renal disease after diabetes mellitus. After discussing the pathophysiology of hypertensive nephropathy, the 'classic' view of hypertensive nephrosclerosis entailing hyalinization, and sclerosis of interlobular and afferent arterioles, we examined the changes occurring in the glomerulus and tubulo-interstitium and the studies that investigated the role of EMT and its molecular mechanisms in hypertensive kidney disease. Finally, we examined the reasons why some studies failed to provide solid evidence for renal EMT in hypertension.

Contrast-enhanced ultrasonography for assessment of tubular atrophy/interstitial fibrosis in immunoglobulin A nephropathy: a preliminary clinical study

PURPOSE

To investigate the potential of contrast-enhanced ultrasonography (CEUS) for evaluating the severity of tubular atrophy/interstitial fibrosis (TA/IF) in immunoglobulin A nephropathy (IgAN) patients.

MATERIALS AND METHODS

A total of 80 patients with IgAN and 33 healthy adults were investigated. Patients were divided into three groups according to the TA/IF (T) grade of the Oxford classification: T0 (n = 28), T1 (n = 35), and T2 (n = 17). Patients and control subjects underwent conventional ultrasound (US) and CEUS. Time-intensity curves of CEUS were drawn for regions of interest located in the renal cortex and medulla using QLab software. Conventional US and CEUS quantitative parameters were analyzed. One-way analysis of variance (ANOVA), binary logistic regression, and receiver operating characteristic (ROC) curves were used.

RESULTS

There were no significant differences in renal size, cortical thickness, and medullary perfusion parameters (P > 0.05), whereas the differences in peak intensity (PI), area under the time-intensity curve (AUC) and wash-in slope (WIS) of cortical perfusion parameters between the control subjects and patients were significant (P < 0.05). PI was significantly lower with the increasing degree of T (P < 0.05). PI was associated independently with the degree of T in IgAN patients (P < 0.05). ROC analysis revealed that using the optimal cutoff values of 15.38 dB for diagnosis of T0-T1 (sensitivity 83.30% and specificity 63.00%) and 14.69 dB for diagnosis of T2 (sensitivity 100.00% and specificity 66.70%), the corresponding areas under the ROC curve were found to be 0.782 and 0.952, respectively.

CONCLUSIONS

CEUS can potentially be used as a noninvasive imaging marker to evaluate the severity of TA/IF in IgAN patients.

Prediction of Tubulointerstitial Injury in Chronic Kidney Disease Using a Non-Invasive Model: Combination of Renal Sonography and Laboratory Biomarkers

The goal of the study described here was to evaluate the degree of tubulointerstitial injury in patients with chronic kidney disease (CKD) using a more accurate model that combines renal sonographic parameters and laboratory biomarkers. A total of 308 patients were enrolled. The study protocol included conventional ultrasound, contrast-enhanced ultrasonography and renal biopsy. CKD patients were divided into normal and mild (≤25%), moderate (26%-50%) and severe (>50%) tubulointerstitial injury groups. We created a model comprising peak intensity, time to peak, urinary retinol-binding protein and β₂-microglobulin that could discriminate severe (>50%) tubulointerstitial injury. The area under the receiver operating characteristic curve of this model was 0.832, which had better accuracy than other individual indexes, and the sensitivity and specificity were 74.2% and 82.8%, respectively. Therefore, this model may be used to evaluate the severity of tubulointerstitial injury and may have the potential to serve as an effective auxiliary method to help nephrologists evaluate patients with CKD.

Transcriptomic changes in human renal proximal tubular cells revealed under hypoxic conditions by RNA sequencing

Chronic hypoxia often occurs among patients with chronic kidney disease (CKD). Renal proximal tubular cells may be the primary target of a hypoxic insult. However, the underlying transcriptional mechanisms remain undefined. In this study, we revealed the global changes in gene expression in HK‑2 human renal proximal tubular cells under hypoxic and normoxic conditions. We analyzed the transcriptome of HK‑2 cells exposed to hypoxia for 24 h using RNA sequencing. A total of 279 differentially expressed genes was examined, as these genes could potentially explain the differences in HK‑2 cells between hypoxic and normoxic conditions. Moreover, 17 genes were validated by qPCR, and the results were highly concordant with the RNA seqencing results. Gene Ontology and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analyses were performed to better understand the functions of these differentially expressed genes. The upregulated genes appeared to be significantly enriched in the pathyway of extracellular matrix (ECM)-receptor interaction, and in paticular, the pathway of renal cell carcinoma was upregulated under hypoxic conditions. The downregulated genes were enriched in the signaling pathway related to antigen processing and presentation; however, the pathway of glutathione metabolism was downregulated. Our analysis revealed numerous novel transcripts and alternative splicing events. Simultaneously, we also identified a large number of single nucleotide polymorphisms, which will be a rich resource for future marker development. On the whole, our data indicate that transcriptome analysis provides valuable information for a more in depth understanding of the molecular mechanisms in CKD and renal cell carcinoma.

Cadherin expression, vectorial active transport, and metallothionein isoform 3 mediated EMT/MET responses in cultured primary and immortalized human proximal tubule cells

BACKGROUND

Cultures of human proximal tubule cells have been widely utilized to study the role of EMT in renal disease. The goal of this study was to define the role of growth media composition on classic EMT responses, define the expression of E- and N-cadherin, and define the functional epitope of MT-3 that mediates MET in HK-2 cells.

METHODS

Immunohistochemistry, microdissection, real-time PCR, western blotting, and ELISA were used to define the expression of E- and N-cadherin mRNA and protein in HK-2 and HPT cell cultures. Site-directed mutagenesis, stable transfection, measurement of transepithelial resistance and dome formation were used to define the unique amino acid sequence of MT-3 associated with MET in HK-2 cells.

RESULTS

It was shown that both E- and N-cadherin mRNA and protein are expressed in the human renal proximal tubule. It was shown, based on the pattern of cadherin expression, connexin expression, vectorial active transport, and transepithelial resistance, that the HK-2 cell line has already undergone many of the early features associated with EMT. It was shown that the unique, six amino acid, C-terminal sequence of MT-3 is required for MT-3 to induce MET in HK-2 cells.

CONCLUSIONS

The results show that the HK-2 cell line can be an effective model to study later stages in the conversion of the renal epithelial cell to a mesenchymal cell. The HK-2 cell line, transfected with MT-3, may be an effective model to study the process of MET. The study implicates the unique C-terminal sequence of MT-3 in the conversion of HK-2 cells to display an enhanced epithelial phenotype.

The level of urinary α1 microglobulin excretion is a useful marker of peritubular capillaritis in antineutrophil cytoplasmic antibody associated vasculitis

BACKGROUND

Antineutrophil cytoplasmic antibody (ANCA) associated vasculitis affects small vessels in the kidney (i.e., arterioles, glomerular or peritubular capillaries, or venules). Although crescentic glomerulonephritis is a common histological finding, the incidence of peritubular capillaritis (PTC) or arteriolitis is unclear. Moreover, the laboratory data that reflect the degree of renal histological damage and distinguish between PTC and arteriolitis have not yet been clarified.

METHODS

We investigated laboratory data and histological findings from 11 patients diagnosed with ANCA-associated vasculitis (2 men and 9 women, mean age 70.3 ± 3.3 years) whose renal biopsies were performed between 2009 and 2014.

RESULTS

All patients were positive for myeloperoxidase (MPO)-ANCA. PTC or arteriolitis was detected in six patients (54.5 %), respectively. The only significant positive relationship between laboratory data and histological findings observed was that between levels of urinary α1 microglobulin (u-α1MG) excretion and the percentage of tubular atrophy and interstitial fibrosis (r = 0.67, p = 0.035). No significant differences in laboratory data were found between patients with or without arteriolitis. However, the levels of u-α1MG excretion were significantly higher in patients with PTC than in those without PTC (75.2 ± 19.5 vs. 15.0 ± 3.6 mg/dl, p = 0.035).

CONCLUSION

PTC or arteriolitis occurs at a high rate independently of crescentic glomerulonephritis in ANCA-associated vasculitis patients. The levels of u-α1MG excretion reflect the degrees of tubular atrophy and interstitial fibrosis. Moreover, high levels of u-α1MG excretion suggest that PTC is more likely than arteriolitis in ANCA-associated vasculitis patients.

Pathophysiology of the diabetic kidney

Diabetes mellitus contributes greatly to morbidity, mortality, and overall health care costs. In major part, these outcomes derive from the high incidence of progressive kidney dysfunction in patients with diabetes making diabetic nephropathy a leading cause of end-stage renal disease. A better understanding of the molecular mechanism involved and of the early dysfunctions observed in the diabetic kidney may permit the development of new strategies to prevent diabetic nephropathy. Here we review the pathophysiological changes that occur in the kidney in response to hyperglycemia, including the cellular responses to high glucose and the responses in vascular, glomerular, podocyte, and tubular function. The molecular basis, characteristics, and consequences of the unique growth phenotypes observed in the diabetic kidney, including glomerular structures and tubular segments, are outlined. We delineate mechanisms of early diabetic glomerular hyperfiltration including primary vascular events as well as the primary role of tubular growth, hyperreabsorption, and tubuloglomerular communication as part of a "tubulocentric" concept of early diabetic kidney function. The latter also explains the "salt paradox" of the early diabetic kidney, that is, a unique and inverse relationship between glomerular filtration rate and dietary salt intake. The mechanisms and consequences of the intrarenal activation of the renin-angiotensin system and of diabetes-induced tubular glycogen accumulation are discussed. Moreover, we aim to link the changes that occur early in the diabetic kidney including the growth phenotype, oxidative stress, hypoxia, and formation of advanced glycation end products to mechanisms involved in progressive kidney disease.

Targeting the epithelial cells in fibrosis: a new concept for an old disease

Fibrosis, which affects millions of individuals worldwide, is a leading cause of organ failure. For 40 years myofibroblasts have been recognized to be the key cellular players in fibrosis. Currently, several pharmaceutical targets are under investigation that may contribute to the activation of myofibroblasts. Recent preclinical and clinical evidence suggests that other components in the fibrotic microenvironment can trigger myofibroblast activation, providing new targets for pharmaceutical intervention. Epithelial cells may represent the most promising cellular phenotype that could be exploited in the design of new anti-fibrotic medicines through their paracrine action on myofibroblasts. The present review briefly highlights this hypothesis and discusses some interesting related pharmacological targets.

Epithelial-mesenchymal crosstalk alteration in kidney fibrosis

The incidence of chronic kidney diseases (CKD) is constantly rising, reaching epidemic proportions in the western world and leading to an enormous threat, even to modern health-care systems, in industrialized countries. Therapies of CKD have greatly improved following the introduction of drugs targeting the renin-angiotensin system (RAAS) but even this refined pharmacological approach has failed to stop progression to end-stage renal disease (ESRD) in many individuals. In vitro historical data and recent new findings have suggested that progression of renal fibrosis might occur as a result of an altered tubulo-interstitial microenvironment and, more specifically, as a result of an altered epithelial-mesenchymal crosstalk. Here we the review biological findings that support the hypothesis of an altered cellular crosstalk in an injured local tubulo-interstitial microenvironment leading to renal disease progression. Copyright © 2012 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Hypoxia decreases podocyte expression of slit diaphragm proteins

Background

Chronic hypoxia contributes to progressive tubulointerstitial injury and, consequently, renal failure. However, the effect of hypoxia on glomerular podocytes, which are integral to the slit diaphragm complex and responsible for selectivity of the glomerular filtration barrier, has not been completely determined.

Methods

Conditionally immortalized mouse podocyte cells were exposed to hypoxic (1% O₂) or normoxic (room air) conditions for 24, 48, or 72 hours, after which cell viability was determined by MTT assay. Cells were stained with podocin and phalloidin to determine podocin and intracellular actin distribution. Expression of synaptopodin, CD2-associated protein (CD2AP), NcK, transforming growth factor-β1 (TGF-β1), hypoxia-inducible factor (HIF-1α) were evaluated by real-time polymerase chain reaction.

Results

Podocytes exposed to hypoxia had significantly reduced viability at 48 (87%) and 72 hours (66%). There was disarrangement of intracellular filament actin by phalloidin staining, a 30% weaker fluorescence intensity by podocin staining, significantly reduced expression of synaptopodin (12%), CD2AP (42%), NcK (38%), and increased expression of TGF-β1 and P-ERK after hypoxia treatment.

Conclusion

Podocyte exposure to hypoxia leads to reduced viability and SD protein expression, which may explain persistent and/or increasing proteinuria in patients with progressive renal failure. Increased expression of TGF-β1 and P-ERK is associated with apoptosis and fibrosis, which could be the link between hypoxia and glomerular injury.

From acute injury to chronic disease: pathophysiological hypothesis of an epithelial/mesenchymal crosstalk alteration in CKD

Observational clinical studies link acute kidney injury to chronic kidney disease (CKD) progression. The pathophysiological mechanisms that underlie this process are currently unknown but recently published papers suggest that tubular epithelial cells and interstitial mesenchymal cells emerge as a single unit, and their integrity alteration as a whole might lead to renal fibrosis and CKD. The present article reviews the biological findings supporting the hypothesis of an altered epithelial/mesenchymal crosstalk in fibrosis development and progression toward CKD.

Improvement of renal function in type 2 diabetic nephropathy

BACKGROUND

Therapeutic failure in preventing renal disease progression in type 2 diabetic nephropathy (DN) is due to a failure in the early detection of DN by microalbuminuria and the inappropriate correction of renal hemodynamic maladjustment secondary to glomerular endothelial dysfunction.

METHODS

Thirty patients associated with normoalbuminuric type 2 DN were subject to the following studies: tubular function by means of fractional excretion of magnesium (FE Mg), vascular function by means of determining the circulating endothelial cell, VEGF, VEGF/TGF B ratio, and intrarenal hemodynamic studies.

RESULTS

FE Mg, circulating endothelial cells, and TGF B were abnormally elevated, and VEGF/TGF B ratio was decreased in these normoalbuminuric patients. The intrarenal hemodynamic study revealed a hemodynamic maladjustment characterized by a preferential constriction at the efferent arteriole and a reduction in peritubular capillary flow. Following treatment with vasodilators, a decrease in efferent arteriolar resistance and increase in peritubular capillary flow as well as glomerular clearance were observed.

CONCLUSION

FE Mg appears to be a more sensitive marker than microalbuminuria for the early detection of DN. Increased endothelial cell injury is reflected by enhanced circulating endothelial cell loss in conjunction with the increased TGF B and the decreased ratio between VEGF and TGF B. This is further supported by the dysfunctioning glomerular endothelium, which is characterized by hemodynamic maladjustment and a reduction in the peritubular capillary flow. A correction of such hemodynamic maladjustment by multidrug vasodilators effectively improves renal perfusion and restores renal function in type 2 DN.

Role of anemia in progression of chronic kidney disease

Anemia is a well-known consequence of chronic kidney disease (CKD), and its prevalence progressively increases when the estimated glomerular filtration rate decreases to less than 60 mL/min/1.73 m2. However, analyses of the consequences of anemia and of the mechanisms of progression of CKD suggest that anemia also could contribute to the deterioration of kidney function. This hypothesis is based mostly on experimental data that imply that hypoxia of tubular cells plays an important role in tubulointerstitial damage associated with CKD and, thus, in the progression of renal failure. It also is supported by the fact that red blood cells represent a major antioxidant component of blood and that oxidative stress appears to contribute to glomerulosclerosis and tubulointerstitial damage. In humans, post hoc analysis of the Reduction of End points in non insulin-dependent diabetes mellitus (NIDDM) with the Angiotensin II Antagonist Losartan study and analyses of smaller prospective cohorts of CKD patients have shown that anemia is an independent risk factor for progression of CKD. In addition, 3 small randomized studies have suggested that anemia correction could slow the progression of CKD. Thus, the existence of a relationship between anemia and progression of CKD is not only plausible biologically, but also is supported by observational studies and by small intervention studies. However, only a large, randomized, prospective trial will be able to establish if anemia correction can slow the progression of CKD effectively.

Enhanced anti-fibrotic activity of plasmid DNA expressing small interference RNA for TGF-beta type II receptor for a mouse model of obstructive nephropathy by cationized gelatin prepared from different amine compounds

The objective of this study is to increase the transfection efficiency of a plasmid DNA expressing small interference RNA (siRNA) for transforming growth factor-beta receptor (TGF-betaR) by various cationized gelatins of non-viral carrier and evaluate the anti-fibrotic effect with a mouse model of unilateral ureteral obstruction (UUO). Ethylenediamine, putrescine, spermidine or spermine was chemically introduced to the carboxyl groups of gelatin for the cationization. The plasmid DNA of TGF-betaR siRNA expression vector with or without complexation of each cationized gelatin was injected to the left kidney of mice via the ureter to prevent the progression of renal fibrosis of UUO mice. Irrespective of the type of cationized gelatin, the injection of plasmid DNA-cationized gelatin complex significantly decreased the renal level of TGF-betaR over-expression and the collagen content of mice kidney, in marked contrast to free plasmid DNA injection. It is concluded that retrograde injection of TGF-betaR siRNA expression vector plasmid DNA complexed with the cationized gelatin is available to suppress the progression of renal interstitial fibrosis.

Delivery of plasmid DNA expressing small interference RNA for TGF-beta type II receptor by cationized gelatin to prevent interstitial renal fibrosis

Renal interstitial fibrosis is the common pathway of chronic renal disease, while it causes end-stage renal failure. Transforming growth factor-beta (TGF-beta) is well recognized to be one of the primary mediators to induce accumulation of extracellular matrix (ECM) in the fibrotic area. Therefore, it is expected that local suppression of TGF-beta receptor (TGF-betaR) is one of the crucial strategies for anti-fibrotic therapy. The objective of this study is to investigate feasibility of small interference RNA (siRNA) for TGF-betaR in the selective degradation of TGF-betaR mRNAs, resulting in fibrotic inhibition. A plasmid DNA of TGF-betaR siRNA expression vector with or without complexation of a cationized gelatin was injected to the left kidney of mice via the ureter. Unilateral ureteral obstruction (UUO) was performed for the injected mice to evaluate the anti-fibrotic effect. The injection of plasmid DNA-cationized gelatin complex significantly decreased the level of TGF-betaR and alpha-smooth muscle actin (alpha-SMA) over-expression, the collagen content of mice kidney, and the fibrotic area of renal cortex, in contrast to free plasmid DNA injection. It is concluded that retrograde injection of TGF-betaR siRNA expression vector plasmid DNA complexed with the cationized gelatin is available to suppress progression of renal interstitial fibrosis.

Activation of tubular epithelial cells by mesangial-derived TNF-alpha: glomerulotubular communication in IgA nephropathy

BACKGROUND

IgA nephropathy (IgAN), characterized by mesangial IgA deposition, runs a variable clinical course with tubulointerstitial damage and renal failure in no less than 30% of patients. Histologically, IgA is rarely detected in renal tubules. The direct toxicity by IgA on renal tubules remains uncertain. We hypothesize that mediators released from human mesangial cells (HMC) triggered by IgA deposition may lead to activation of proximal tubular epithelial cells (PTEC).

METHODS

The binding of IgA to PTEC or HMC was assessed by flow cytometry. IgA-HMC medium was prepared by collecting the spent medium in which growth arrested HMC were incubated with IgA isolated from patients with IgAN, healthy control subjects, or other nephritic control patients. PTEC was cultured with the IgA-HMC medium in the presence or absence of neutralizing antibodies to TNF-alpha, IL-1beta, TGF-beta, or PDGF. Gene expression and protein synthesis of TNF-alpha, MIF, or ICAM-1 by PTEC were determined by RT-PCR and ELISA, respectively.

RESULTS

The binding of IgA isolated from patients with IgAN to PTEC was increased when compared to binding of IgA from healthy control subjects (P < 0.005). However, the binding to PTEC was less than one tenth that of HMC in IgAN. The binding to PTEC was not mediated through known IgA receptors, as shown by competitive binding assays and gene expression of the receptors. Despite the in vitro binding, PTEC cultured with isolated IgA exhibited no increased cell proliferation or enhanced synthesis of TNF-alpha, MIF, or sICAM-1. However, when PTEC were cultured with IgA-HMC medium prepared from IgAN patients, there was enhanced proliferation of PTEC (P < 0.001) and increased synthesis of TNF-alpha, MIF, and sICAM-1 when compared with PTEC cultured with IgA-HMC medium from control subjects (P < 0.001). The synthesis of MIF and sICAM-1 by PTEC cultured with IgA-HMC medium was reduced by neutralizing antibodies to TNF-alpha (P < 0.001) but not by neutralizing antibodies to IL-1beta, TGF-beta, or PDGF.

CONCLUSION

Our finding implicates that TNF-alpha released from the mesangium after IgA deposition activates renal tubular cells. The glomerulotubular communication could play an important role in the pathogenesis of tubulointerstitial damage in IgAN.

Dysregulation of renal MMP-3 and MMP-7 in canine X-linked Alport syndrome

Matrix metalloproteinases (MMPs) play an important regulatory role in many biological and pathological processes and their specific role in Alport syndrome (AS) is not yet clearly defined. In this study, the naturally occurring canine X-linked AS was used to demonstrate a potential role for MMP-3 and MMP-7 in Alport renal pathogenesis. Recently, we demonstrated that the expression of MMP-2, MMP-9 and MMP-14 was upregulated in the renal cortex of dogs with a spontaneous form of XLAS. In the present study, we examined necropsy samples of renal cortex from normal and XLAS dogs for MMP-3 and MMP-7 as they have the potential to activate MMP-2 and MMP-9. Immunohistochemical analysis showed strong immunostaining for both MMP-3 and MMP-7 in the interstitial space of XLAS kidneys, while virtually no immunostaining was observed in similar fields from normal dogs. RT-PCR and casein zymography confirmed that both mRNA transcripts and activities of MMP-3 and MMP-7 are elevated in XLAS kidneys. The induction of these MMPs likely contributes to tissue destruction associated with the fibrogenic process, while augmenting the activation of MMP-2 and MMP-9 by MMP-3 and MMP-7 in XLAS. Thus, these data further implicate a role for the MMPs in progressive renal pathogenesis associated with AS.

Targeting of Plasmid DNA to Renal Interstitial Fibroblasts by Cationized Gelatin

Renal interstitial fibrosis is the common pathway of chronic renal disease, while it causes end-stage renal failure. A lot of cytokines and biologically active substances are well recognized to be the candidates of primary mediators to induce accumulation of extracelluar matrix (ECM) in the interstitial fibrotic area. Interstitial fibroblasts are played a crucial role in the accumulation of excess ECM during renal interstitial fibrogenesis. Therefore, the targeting of therapeutic drugs and genes to interstitial renal fibroblasts is effective in suppressing the progress of interstitial renal failure. However, despite various approaches and techniques, few successful results have been reported on the in vivo targeting for interstitial fibroblasts. The objective of this study is to deliver an enhanced green fluorescent protein (EGFP) plasmid DNA, as a model plasmid DNA, into renal interstitial space by a cationized gelatin. After the plasmid DNA with or without complexation of the cationized gelatin was injected to the left kidney of mice via the ureter, unilateral ureteral obstruction (UUO) was performed for the mice injected to induce the renal interstitial fibrosis. When the EGFP plasmid DNA complexed with the cationized gelatin was injected, EGFP expression was observed in the fibroblasts in the interstitial area of renal cortex. It is concluded that the retrograde injection of EGFP plasmid DNA complexed with the cationized gelatin is available to target the interstitial renal fibroblasts which are currently considered as the cell source responsible for excessive ECM synthesis.

9HODE stimulates cell proliferation and extracellular matrix synthesis in human mesangial cells via PPARgamma

Plasma oxidized low-density lipoprotein (OX-LDL) levels are elevated in patients with renal diseases, including diabetic nephropathy. We examined effects of OX-LDL on cell proliferation and extracellular matrix (ECM) production by using normal human mesangial cells. Furthermore, we examined possible involvement of peroxisome proliferator-activated receptor gamma (PPARgamma). Mesangial cell proliferation with OX-LDL, 9-hydroxy-10,12-octadecadienoic acid (9HODE), and 13-hydroxy-9,11-octadecadienoic acid (13HODE), the major components of OX-LDL, were determined by 5-bromo-2'-deoxyuridine (BrdU) or 3-(4,5-dimethylthiazol-2-yl)-2, 5-diphenyl tetrazolium bromide (MTT) incorporation. The effect of OX-LDL on mesangial cell proliferation with PD98059 pretreatment was determined by BrdU incorporation. Type IV collagen, fibronectin, and PPARgamma expression with OX-LDL or 9HODE or 13HODE was determined by Western blotting. Type IV collagen expression with antisense oligonucleotide against PPARgamma pretreatment was also determined by Western blotting. The effect of PD98059 pretreatment on PPARgamma expression was determined by Western blotting. In mesangial cells exposed to isolated OX-LDL from human plasma, BrdU incorporation was increased, and this increase was deleted by PD98059. Type IV collagen expression was significantly increased by OX-LDL. 9HODE and 13HODE increased BrdU and MTT incorporation into mesangial cells and also increased expressions of Type IV collagen and fibronection, the major components of ECM. PPARgamma expression in mesangial cells was stimulated by 9HODE. The reduction of PPARgamma synthesis by pretreatment of antisense oligonucleotide against PPARgamma remarkably attenuated Type IV collagen synthesis induced by 9HODE. PPARgamma expression induced by 9HODE was also reduced by PD98059 pretreatment. These findings demonstrate that 9HODE, the major component of OX-LDL, stimulates cell proliferation and ECM production of human mesangial cells. In addition, the stimulatory effects are, at least in part, mediated by PPARgamma, which may exist in downstream of ERK1/2 pathway.

Anemia management and the delay of chronic renal failure progression

Interstitial fibrosis plays a key role in the progression of chronic kidney diseases. Analysis of the biologic effects of erythropoietin and of the pathophysiology of interstitial fibrosis suggest that treatment with epoetin may slow the progression of chronic kidney disease, both by decreasing interstitial fibrosis and by protecting against its consequences. The results of two small prospective studies and of a retrospective one also suggest that treatment with epoetin may have such protective effects.

Gelatinase A (MMP-2) is necessary and sufficient for renal tubular cell epithelial-mesenchymal transformation

Progressive renal interstitial fibrosis and tubular atrophy represent the final injury pathway for all commonly encountered forms of renal disease that lead to end-stage renal failure. It has been recently recognized that myofibroblastic cells are the major contributors to the deposition of interstitial collagens. While there are several potential cellular sources of myofibroblasts, attention has focused on the transformation of the organized tubular epithelium to the myofibroblastic phenotype, a process potently driven both in vitro and in vivo by transforming growth factor-beta1 (TGF-beta1). Integrity of the underlying basal lamina provides cellular signals that maintain the epithelial phenotype, and disruption by discrete proteases could potentially initiate the transformation process. We demonstrate that TGF-beta1 coordinately stimulates the synthesis of a specific matrix metalloproteinase, gelatinase A (MMP-2), and its activator protease, MT1-MMP (MMP-14), and that active gelatinase A is absolutely required for epithelial-mesenchymal transformation induced by TGF-beta1. In addition, purified active gelatinase A alone is sufficient to induce epithelial-mesenchymal transformation in the absence of exogenous TGF-beta1. Gelatinase A may also mediate epithelial-mesenchymal transformation in a paracrine manner through the proteolytic generation of active TGF-beta1 peptide. MT1-MMP and gelatinase A were co-localized to sites of active epithelial-mesenchymal transformation and basal lamina disruption in the rat remnant kidney model of progressive renal fibrosis. These studies indicate that a discrete matrix metalloproteinase, gelatinase A, is capable of inducing the complex genetic rearrangements that characterize renal tubular epithelial-mesenchymal transformation.

Determination of renal porphyrin handling in rats suffering from different kinds of chronic renal failure (CRF): uranyl nitrate (UN) induced fibrosis or 5/6-nephrectomy (5/6NX)

The renal handling of porphyrins is reported to be a sensitive marker for chronic renal failure (CRF) for two reasons: heme is synthesised in proximal tubules and porphyrins are reabsorbed in the renal proximal tubule by apical peptide transporter PEPT 2. Two different models of CRF in female Wistar rats have been used for investigation of renal porphyrin handling: (1) single administration of uranyl nitrate (UN; 0.5 mg/100 g b.wt.) and (2) 5/6 nephrectomy (5/6NX). Renal clearance experiments were performed at weeks 2 and 10 after the onset of CRF. The concentrations of porphyrin intermediates (uroporphyrin I and III, coproporphyrin I and II, heptaporphyrin, and pentaporphyrin) were measured by HPLC with fluorescence detection. Both after UN and 5/6NX a significant reduction of body weight occurred. The kidney weight was enhanced 2 weeks after UN compared to controls (+31%). After 5/6NX, the weight of the remnant kidney was 44% (2nd week) and 140% (10th week) higher compared to one control kidney. Urine volumes and GFR were significantly reduced at week 2 and 10 after 5/6NX, but at week 10 after UN values were comparable to controls. Two weeks after UN and 5/6NX the concentrations of heptaporphyrin was moderately decreased in renal tissue whereas after 10 weeks the concentrations of most porphyrins were increased in the kidney. The plasma levels of free porphyrins were only slightly enhanced (week 2). The renal excretion of porphyrins was initially slightly reduced in both models, whereas it increases 10 weeks after UN, but it remained reduced 10 weeks after 5/6NX. UN induces tubulointerstitial fibrosis including atrophic glomeruli, whereas 5/6NX was characterized by distinct proteinuria, dilated tubules containing hyaline casts. A modulation of porphyrin metabolism in the kidney seems first of all to be responsible for UN effect on renal porphyrin handling. Summing up the 5/6NX results, both reduction in intact renal tissue mass and a modification of enzymes involved in heme biosynthesis by uraemic toxins are responsible for accumulation of porphyrins in renal tissue. After 5/6NX reduced excretion of porphyrins into urine and enhanced porphyrin concentrations in the kidney indicate more a damage of renal porphyrin biosynthesis than changes in their reabsorption.

Increased expression of MMP-2, MMP-9 (type IV collagenases/gelatinases), and MT1-MMP in canine X-linked Alport syndrome (XLAS)

BACKGROUND

Alport syndrome is a group of genetic disorders resulting from mutations in either the alpha3(IV), alpha4(IV) or alpha5(IV) collagen chains. The disease is characterized by a progressive glomerulonephritis, usually associated with a high-frequency specific sensorineural hearing loss, dot and fleck retinopathy, and lens abnormalities. Dogs with naturally occurring genetic disorders of basement membrane collagen (type IV) may serve as animal models of Alport syndrome. In this study, a well-characterized naturally occurring canine model was employed to demonstrate a potential role for matrix metalloproteinases (MMPs) in Alport renal disease pathogenesis.

METHODS

Adolescent male dogs that developed renal failure were euthanized and necropsied. Clinicopathologic features of the disease were characterized, and kidneys from normal and Alport dogs were analyzed by gelatin zymography, Western blotting, in situ zymography, immunohistology, and by reverse transcription polymerase chain reaction (RT-PCR) for expression of MMP-2, MMP-9, and membrane type 1-MMP (MT1-MMP).

RESULTS

Affected dogs developed proteinuria and rapidly progressive juvenile-onset chronic renal failure. The activities of MMP-2 and MMP-9 were significantly induced in Alport kidney. In situ zymography confirmed elevated active metalloproteinases in kidney cryosections of affected dogs. The mRNAs encoding MMP-2, MMP-9 and MT1-MMP were also increased in Alport dogs suggesting that elevated expression of MMPs reflects events in the progression of Alport syndrome in dogs.

CONCLUSION

Elevated expression of MMP-2, MMP-9, and MT1-MMP is observed in fibrotic renal cortex from X-linked Alport syndrome dogs. These findings suggest that MMPs may play an important role in matrix accumulation associated with progressive renal scarring in this model.

Structural and functional changes in heparan sulfate proteoglycan expression associated with the myofibroblastic phenotype

The principal cells implicated as the source of the extracellular matrix in areas of progressive fibrosis are fibroblasts with the phenotypic appearance of myofibroblasts. This report describes differences in heparan sulfate proteoglycan expression between myofibroblasts and normal fibroblasts, associated with impaired responses to fibroblast growth factor-2 (FGF-2). Although both cell types responded to platelet-derived growth factor, myofibroblasts, unlike fibroblasts, did not proliferate to FGF-2. A response was acquired, however, when myofibroblasts were incubated with FGF-2 in the presence of heparan sulfate (HS) and heparin. Selective digestion with pronase, NaOH/NaBH(4), heparinase I, or low pH nitrous acid showed that each HS-glycosaminoglycan region comprised a pronase-resistant peptide separating two HS chains. The HS-glycosaminoglycan chains from myofibroblasts were larger (K(av), 0.32; molecular weight, 50 kd) than those from fibroblasts (K(av), 0.4; molecular weight, 33 kd), although their disaccharide composition was identical. The chains from myofibroblasts, however, contained three, compared to two, heparinase 1-resistant sequences separated by larger contiguous areas of low sulfation. Furthermore, although there was no difference in FGF-2-binding affinity between the two cell types, the chains secreted by myofibroblasts had twice the binding capacity of those from fibroblasts. Thus, it is likely that the difference in response to FGF-2 is because of a difference in FGF-2 sequestration and receptor interaction with FGF-2-HS complexes. A comparative investigation into HS fine structure is being undertaken to examine these findings in more detail.

Classification of renal proteinuria: a simple algorithm

Total protein, albumin, alpha1-microglobulin, and immunoglobulin G (IgG) were analyzed in 1,622 urine samples without Bence-Jones proteinuria or gross hematuria. There was correlation with the histological picture obtained on renal biopsy in 61 patients. We established 24-h reference intervals for alpha1-microglobulin and IgG on 659 urine samples with total protein and albumin excretion rates below 100 mg/24 h and 30 mg/24 h, respectively, and creatinine clearance above 80 ml/min. The central 95% reference interval was found to be between 4 and 17 mg/24 h for alpha1-microglobulin and between 3 and 8.5 mg/24 h for IgG. In 80 urine samples with albumin excretion rate above 30 mg/24 h and alpha1-microglobulin and IgG within their reference intervals, we analyzed the 95% central interval of the distribution of the IgG/albumin ratios, and it was found to be within 0.01 and 0.20 (0.90 confidence interval: 0.17-0.24). Proteinuria was considered to be of the selective glomerular type if the albumin excretion rate was abnormal and the IgG/albumin ratio was under 0.20, even when the IgG excretion was within a pathological range. For the classification of proteinuria as predominantly tubular, we estimated the alpha1-microglobulin/albumin ratio in 173 urine samples with normal excretion rates of albumin and IgG and pathological excretion of alpha1-microglobulin. The discriminating value of 0.91 (0.90 confidence interval: 0.78-1.08) was accepted in order to define proteinuria of a tubular origin in the presence of a pathological albumin excretion rate. The association between albumin and IgG excretion rates and tubular reabsorption of the alpha1-microglobulin normally filtered by the glomerulus was studied in 33 urine samples from patients with no histologically significant tubulo-interstitial or vascular disease and a serum creatinine concentration below 141 pmol/l. The optimal curve-fitting function between albumin plus IgG and alpha1-microglobulin excretion rates was of the quadratic type (r = 0.927). Mixed proteinuria was considered when both, albumin and alpha1-microglobulin excretion rates were pathological and could not be included in the previously described groups.

TGF-beta1 is an autocrine mediator of renal tubular epithelial cell growth and collagen IV production

Recent studies in cultured cells have provided evidence that a variety of pathobiologic stimuli, including high glucose, angiotensin II, and thromboxane A(2), trigger a signaling pathway leading to autocrine induction of TGF-beta1. TGF-beta1 production through this pathway may profoundly affect cell growth, matrix synthesis, and response to injury. This study examines the role of autocrine versus exogenously added TGF-beta1 in cellular proliferation and collagen IV production, critical targets of TGF-beta1 signaling, using renal cells derived from TGF-beta1 knockout (KO) animals or wild-type (WT) controls. Growth of WT and KO cells was assessed by cell counting and [(3)H]thymidine uptake. Basal and TGF-beta1-stimulated collagen production was assessed by Northern and Western blotting; transcriptional activity of the alpha1(IV) collagen gene was assessed by transient transfection analysis. KO cells grew at a faster rate than WT cells carefully matched for plating density and passage number. This increased growth rate was paralleled by increases in [(3)H]thymidine uptake. KO cells expressed lower levels of the cell cycle inhibitors p21 and p27 than WT cells. KO cells failed to express TGF-beta1, as expected. Basal TGF-beta3 mRNA levels were higher in KO cells than in WT cells. WT cells expressed higher basal levels of TGF-beta2 mRNA than KO cells. Basal alpha1(IV) and alpha2(IV) collagen mRNA and protein expression were significantly lower in KO cells than WT cells. Administration of exogenous TGF-beta1 induced collagen IV production in both KO and WT cells. Although basal transcriptional activity of an alpha1(IV) collagen-CAT construct was lower in KO cells than WT cells, administration of exogenous TGF-beta1 was associated with significant increases in transcriptional activity of this construct in both KO and WT cells. These studies provide evidence that autocrine production of TGF-beta1 may play a critical role in regulation of growth and basal collagen IV production by renal tubular epithelial cells.

Regulation of endothelin-1 and transforming growth factor-beta1 production in cultured proximal tubular cells by albumin and heparan sulphate glycosaminoglycans

BACKGROUND

Both endothelin-1 (ET-1) and transforming growth factor beta 1 (TGF-beta1) have been implicated in the progression of interstitial fibrosis. In the present study we enquired if albumin influences the production of these factors in cultured human proximal tubular epithelial cells (PTEC) and if heparan sulphate glycosaminoglycans (HS-GAG) can inhibit this production.

METHODS

ET-1 and TGF-beta1 production in supernatants of PTEC was measured by RIA and ELISA respectively. In addition semi-quantitative reverse transcription polymerase chain reaction (RT-PCR) was performed to study differences in ET-1 and TGF-beta1 mRNA expression. To demonstrate ET-1 or TGF-beta1 binding to heparin or HS-GAG, binding studies by means of dot blot analysis were carried out.

RESULTS

TGF-beta1 and ET-1 were both produced in different concentrations, depending on the PTEC culture tested. Human serum albumin (HSA) up-regulated the production of both factors in a time and dose dependent fashion. The production of these factors was inhibited by heparin under basal and stimulatory conditions. ET-1 production was only inhibited by HS-GAG with a high degree of sulphation. For the inhibition of TGF-beta1 production, the sulphation of HS-GAG was less critical. TGF-beta1, but not ET-1 mRNA expression was inhibited by HS-GAG. Inhibition of sulphation of cell surface HS-GAG resulted in the inhibition of ET-1 but not TGF-beta1 production. Both factors were able to bind to HS-GAG, although this required different amounts of HS-GAG sulphation for each factor.

CONCLUSIONS

Our data demonstrate that in PTEC the release of pro-fibrogenic factors can be inhibited by HS-GAG. This may explain to some extent the beneficial effect of heparin in the treatment of interstitial fibrosis.

Transforming growth factor-beta receptor types I and II are expressed in renal tubules and are increased after chronic unilateral ureteral obstruction

Transforming growth factor-beta (TGF-beta) is a profibrotic cytokine which has been implicated in the renal fibrosis which follows unilateral ureteral obstruction (UUO) in the rat. TGF-beta receptor type I (TGF-RI) and TGF-beta receptor type II (TGF-RII) are part of the complex which mediates the response to TGF-beta. We sought to determine if TGF-RI and TGF-RII are found in the kidney, and if their expression is changed as a result of UUO. Polymerase chain reaction (PCR) was used to determine expression of mRNA for TGF-RI and TGF-RII in the kidney. Immunoperoxidase was used to localize and quantify the expression of these receptors at 3, 7, 14, 21 and 28 days after UUO, and in sham-operated animals. Expression of mRNA for TGF-RI and TGF-RII was demonstrated in sham operated, obstructed and contralateral unobstructed kidneys using PCR. Using immunoperoxidase, a uniform distribution of TGF-RI and TGF-RII was found in cortical tubules of sham operated kidneys, whereas medullary tubules showed a patchy TGF-RI distribution and no TGF-RII staining. After UUO, an increased tubular expression of TGF-RI and TGF-RII was noted in both obstructed and contralateral kidneys compared to sham operated kidneys. No staining for either TGF-RI or TGF-RII was noted in glomeruli, vasculature or interstitial cells. TGF-beta receptors I and II were found exclusively in renal tubules and were shown to increase in both the obstructed and contralateral kidneys relative to sham operated animals. Upregulation of TGF-beta receptors in both kidneys suggests that TGF-beta may contribute to the fibrotic response in the obstructed kidney and the hypertrophic response of the contralateral kidney.

Hypoxia promotes fibrogenesis in human renal fibroblasts

BACKGROUND

The mechanisms underlying progressive renal fibrosis are unknown, but the common association of fibrosis and microvascular loss suggests that hypoxia per se may be a fibrogenic stimulus.

METHODS

To determine whether human renal fibroblasts (HRFs), the primary matrix-producing cells in the tubulointerstitium, possess oxygen-sensitive responses relevant to fibrogenesis, cells were exposed to 1% O2 in vitro.

RESULTS

Hypoxia simultaneously stimulated extracellular matrix synthesis and suppressed turnover with increased production of collagen alpha1(I) (Coll-I), decreased expression of collagenase, and increased tissue inhibitor of metalloproteinase (TIMP)-1. These effects are time dependent, require new RNA and protein synthesis, and are specific to hypoxia. The changes in Coll-I and TIMP-1 gene expression involve a heme-protein O2 sensor and protein kinase- and tyrosine kinase-mediated signaling. Although hypoxia induced transforming growth factor-beta1 (TGF-beta1), neutralizing anti-TGF-beta1-antibody did not block hypoxia-induced Coll-I and TIMP-1 mRNA expression. Furthermore, hypoxic-cell conditioned-medium had no effect on the expression of these mRNAs in naive fibroblasts, suggesting direct effects on gene transcription. Transient transfections identified a hypoxia response element (HRE) in the TIMP-1 promoter and demonstrated HIF-1-dependent promoter activation by decreased ambient pO2.

CONCLUSIONS

These data suggest that hypoxia co-ordinately up-regulates matrix production and decreases turnover in renal fibroblasts. The results support a role for hypoxia in the pathogenesis of fibrosis and provide evidence for novel, direct hypoxic effects on the expression of genes involved in fibrogenesis.

Identification and kinetics of leukocytes after severe ischaemia/reperfusion renal injury

BACKGROUND

Leukocyte adhesion/infiltration in response to renal ischaemia/reperfusion (I/R) injury is a well-known but poorly understood phenomenon. The identification, kinetics, and exact role of these inflammatory cells in I/R injury and regeneration are still matters of debate.

METHODS

Uninephrectomized rats were submitted to 60 min renal ischaemia by clamping of renal vessels.

RESULTS

Severe acute renal failure was observed, with maximum functional impairment on day 2. By 12 h after the ischaemic event, up to 80% of proximal tubular cells in the outer stripe of outer medulla (OSOM) were already severely damaged. Proliferation (proliferating cell nuclear antigen (PCNA) staining) started after 24 h, reaching maximum activity on day 3. Regeneration of tubular morphology started on the 3rd day, and after 10 days 50% of tubules had regenerated completely. Interstitial leukocytes (OX-1 immunohistochemical staining) were already prominent at day 1, thereafter gradually increasing with time. The so-called neutrophil-specific identification methods (myeloperoxidase (MPO), chloroacetate esterase, mAb HIS-48) proved to be non-specific, since they also stained for macrophages, as demonstrated by flow cytometry and the combination of these stainings with the macrophage-specific ED-1 staining. MPO activity was already significantly increased at 1 h post-I/R (439+/-34%, P<0.005), reaching its maximum activity after 12 h of I/R (1159+/-138%, P<0.0005), declining thereafter. On the other hand, neutrophil presence investigated by H&E staining revealed only a few neutrophils in glomeruli, medullary rays, and OSOM at 24 h after the ischaemic event (4.7+/-4.2 cells/mm(2) vs controls=2.3+/-2.0 cells/mm(2) (n.s.)), and remained unchanged over the next 10 days. In contrast, significant monocyte/macrophage adhesion/infiltration (ED-1 staining) occurred at the OSOM at 24 h post-ischaemia (at 24 h, 120+/-46 cells/mm(2) vs. sham=18+/-4 cells/mm(2) (P<0.05)), became prominent at day 5 (1034+/-161 cells/mm(2) vs sham=18+/-18 cells/mm(2) (P<0.05)), and almost disappeared after 10 days. CD4(+) cells (W3/25) gradually increased from day 5, reaching a maximum at day 10. A few CD8(+) cells (OX-8) were apparent from days 3 until 10, but no B-cells (OX-33) were observed.

CONCLUSIONS

After severe warm I/R renal injury, a pronounced acute tubular necrosis occurs during the first 12-24 h in the absence of a marked cellular infiltrate, but with an important renal MPO activity, reflecting the activation of the adhering inflammatory cells (polymorphonuclear cells (PMNs) and mainly monocytes/macrophages). Only later at the time and site (OSOM) of regeneration a sequential accumulation of monocytes/macrophages and T cells becomes prominent, in contrast with the low number of neutrophils found in the kidney during the 10-day post-ischaemic period. The non-specificity of the so-called neutrophil-specific identification methods (MPO activity, naphthol AS-D chloroacetate esterase, or mAb HIS-48 staining), cross-reacting with monocytes/macrophages, explains the controversy in literature concerning the number of PMNs in post-ischaemic injury.

Reactive oxygen species stimulate p44/42 mitogen-activated protein kinase and induce p27(Kip1): role in angiotensin II-mediated hypertrophy of proximal tubular cells

Angiotensin II (AngII) induces G(1) phase arrest and hypertrophy of cultured renal proximal tubular cells. In previous studies, it was shown that these effects depend on oxygen radical-mediated induction of p27(Kip1), an inhibitor of cyclin-dependent kinases. The present study was undertaken to investigate whether mitogen-activated protein (MAP) kinases serve as signaling intermediates between AngII-induced oxidative stress and induction of p27(Kip1). AngII (10(-7) M) induces a biphasic phosphorylation pattern of p44/42 MAP kinase with an early phosphorylation after 2 min and a later, second phosphorylation peak after prolong incubation (12 h) in cultured proximal tubular cells from two different species (MCT and LLC-PK(1) cells). Total protein expression of MAP kinase was not changed by AngII. These phosphorylation patterns of p44/42 MAP kinase caused activation of the enzyme, as detected by phosphorylated MAP substrate Elk-1 after immuno-precipitation of MAP kinase. Exogenous H(2)O(2) also stimulates a biphasic phosphorylation of p44/42 MAP kinase. The flavoprotein inhibitor diphenylene iodinium, as well as the antioxidant N-acetylcysteine, prevented AngII-induced p44/42 MAP kinase phosphorylation, indicating involvement of reactive oxygen species generated by membrane-bound NAD(P)H oxidase. The MAP kinase kinase inhibitor PD98059 completely inhibits AngII-induced p27(Kip1) expression and (3)[H]leucine incorporation into proteins as a previously established marker of cell hypertrophy. PD98059 did not attenuate AngII-stimulated intracellular synthesis of oxygen radicals. Transient transfection with p44/42 MAP kinase antisense, but not sense, phosphorothioate-modified oligonucleotides also prevented AngII-induced MAP kinase phosphorylation, p27(Kip1) expression, and cell hypertrophy. Furthermore, induction of p27(Kip1) by H(2)O(2) was also abolished in the presence of PD98059. Although AngII induces phosphorylation of the stress-activated p38 MAP kinase, inhibition of this enzyme with SB203580 failed to attenuate induced p27(Kip1) expression and hypertrophy. These data provide evidence that AngII- mediated oxygen stress leads to the phosphorylation of p44/42 MAP kinase in proximal tubular cells. Activation of this enzyme is essential for p27(Kip1) expression, G(1) phase arrest, and hypertrophy of proximal tubular cells. These findings may lead to new concepts concerning interference of the development of proximal tubular hypertrophy, which may eventually turn into a maladaptive process in vivo leading ultimately to tubular atrophy and tubulointerstitial fibrosis.

Severe proteinuria, sustained for 6 months, induces tubular epithelial cell injury and cell infiltration in rats but not progressive interstitial fibrosis

BACKGROUND

Sustained proteinuria is reported to be very harmful to the tubulointerstitium, leading to severe interstitial injury. However, it remains unclear whether sustained proteinuria itself is responsible for severe interstitial injury because, in the previously reported models, the development of factors other than proteinuria in tubulointerstitial lesions could not be excluded completely.

METHODS

After treatment to induce immune tolerance to mouse immunoglobulin, 20 rats were injected with anti-rat slit diaphragm monoclonal antibody (mAb) 5-1-6 twice a week for 6 months and were then sacrificed.

RESULTS

mAb 5-1-6 induced massive proteinuria in 11 rats. In nine rats with mild proteinuria, no histological alteration could be detected with light microscopy and immunofluorescence. In nephrotic rats, light microscopy showed minor glomerular abnormalities, with interstitial oedema, tubular epithelial cell degeneration and interstitial cell infiltration. Immunofluorescence revealed increased expression of vimentin and an increased number of OX1-, OX19- and ED1-positive cells. However, we could not detect any accumulation of type I and IV collagen or laminin in the tubulointerstitium. RT-PCR showed that the expression of mRNA for type I collagen was not increased, compared with that in control rats.

CONCLUSIONS

We succeeded in developing a model of persistent nephrosis without severe glomerular abnormalities, nephrectomy or other manoeuvres known to induce disturbed haemodynamics, using an agent without tubulointerstitial toxicity, and considered it to be suitable for investigating the direct toxicity of proteinuria. In this model, isolated massive proteinuria induced interstitial injury. However, the degree of injury was suggested to be much less than that observed in other previously developed models.

Blunted erythropoietin response to anemia in patients with Type 1 diabetes

BACKGROUND

It is known that patients with renal failure have normochromic normocytic anemia due to impaired endogenous erythropoietin (EPO) synthesis. The aim of this work was to determine whether low serum erythropoietin (s-EPO) levels play a role in the pathogenesis of anemia in patients with Type 1 diabetes without overt nephropathy.

METHODS

We included in the study 13 patients with Type 1 diabetes whose Hb levels were <11 g/dl. Blood cell count, s-EPO, urinary albumin excretion rate (AER), HbA(1c), glomerular filtration rate, serum iron, serum ferritin, the presence of neuropathy, retinopathy and nephropathy were determined.

RESULTS

Ten out of 13 patients with anemia (77%) had a blunted EPO response to anemia. All ten patients with low EPO levels had autonomic neuropathy; five had clinical nephropathy but with serum creatinine<1.6 mg/dl. Three patients were treated with rHuEPO and showed an improvement in their anemia after treatment.

CONCLUSION

The majority of patients with Type 1 diabetes who had anemia also had low EPO levels. The pathogenesis of this phenomenon is probably multifactorial. Autonomic neuropathy appears to play a role, but it is not sufficient, per se, to be the only cause. Dysautonomia might enhance the effect of renal damage.

Studies of renal injury III: lipid-induced nephropathy in type II diabetes

Studies of renal injury III: Lipid-induced nephropathy in type II diabetes.

BACKGROUND

Nephrotoxicity from elevated circulating lipids occurs in experimental and clinical situations. We tested the hypothesis that lipid-induced nephropathy causes advanced renal failure in rats with type II diabetes and dyslipidemia.

METHODS

First generation (F1) hybrid rats derived from the spontaneous hypertensive heart failure rat (SHHF/Gmi-fa) and the LA/NIH-corpulent rat (LA/N-fa) were studied for 41 weeks while being on specific diets. Group 1 (14 rats) ingested 11.5% protein, 47.9% fat, and 40.6% carbohydrate. Group 2 (8 rats) ingested 26.9% protein, 16.7% animal fat, and 56.4% carbohydrate, and group 3 (20 rats) ingested 20.2% protein, 40.4% soy and coconut oil, and 39.4% carbohydrate.

RESULTS

Hyperglycemia was more severe in rat groups 1 and 2 than in group 3. In contrast, circulating cholesterol and hydroperoxide levels were highest in group 3, intermediate in group 2, and lowest in group 1. Group 3 had severe renal failure secondary to glomerulosclerosis and tubulointerstitial disease, with striking deposition of the lipid peroxidation stress biomarker 4-hydroxynonenal in glomeruli and renal microvessels. Moreover, in group 3, increased arterial wall thickness also connoted vascular injury. In contrast, the glycoxidation stress biomarkers pentosidine and carboxymethyl-lysine were preferentially localized to renal tubules of hyperglycemic rats in groups 1 and 2 and did not segregate with the most severe renal injury. Glomerular and interstitial fibrosis was accompanied by proportional increases in renal transforming growth factor-beta1 levels, which were threefold higher in the hypercholesterolemic rats of group 3 than in the hyperglycemic rats of group 1.

CONCLUSIONS

Acquisition of non-nodular glomerular sclerosis and tubulointerstitial disease is dependent on lipoxidation stress in rats with type II diabetes. On the other hand, in the absence of hypercholesterolemia, prolonged glycoxidation stress does not appear to be uniquely nephrotoxic.

Peritubular capillary injury during the progression of experimental glomerulonephritis in rats

The functional and morphologic changes occurring in the peritubular capillaries (PTC) of the kidney during the progression of renal disease are not yet completely understood. In this study, the features of PTC disruption observed in a rat anti-glomerular basement membrane-induced glomerulonephritis (GN) model were characterized. Contributions to the progression of the disease made by other interstitial components, including ED-1-positive macrophages and CD3-positive T cells, were also investigated. Within 7 d of inducing GN, severe necrotizing glomerular injuries were observed. Thrombomodulin staining revealed that within 3 to 8 wk, there was a significant (P < 0.001) decline in the number of PTC, accompanied by a marked accumulation of macrophages, T cells, and fibrotic material. By the end of this period, most PTC were severely damaged or lost, and tubulointerstitial scarring was noted in the affected areas. Furthermore, PTC endothelial cell apoptosis occurred concomitantly, as shown by application of terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling methods and electron microscopy. It was presumed that the PTC injury was mediated possibly by the infiltrating macrophages and T cells, which, together with destruction of the PTC structure, correlated significantly with the impairment of renal function. These findings suggest that PTC disruption and the subsequent regression of the capillary network may contribute to the development of the tubulointerstitial injury largely responsible for the renal dysfunction in progressive GN.

Secretion of chemokines and cytokines by human tubular epithelial cells in response to proteins

BACKGROUND

Chronic interstitial scarring contributes to the progression of renal failure in glomerular disease but its cause is unknown. The development of proteinuria could stimulate tubular cells to release cytokines, chemoattractants and matrix proteins into the interstitium, thus contributing to interstitial disease.

METHODS

Polarized human tubular epithelial cells were grown on permeable supports and exposed to serum proteins on their apical surface. The release of tumour necrosis factor alpha(TNFalpha), platelet derived growth factor (PDGF) and monocyte chemoattractant protein-1 (MCP-1) by the cells was measured using immunoassays.

RESULTS

Under control conditions there was polarized release of PDGF-AB with predominant basolateral secretion (basolateral to apical ratio 4.7+/-1.6). MCP-1 release was less polarized (ratio 1. 7+/-0.5). TNFalpha was not detected. Exposure of the cells to normal human serum proteins on their apical side increased basolateral release of PDGF-AB (1.7+/-0.4 fold) and MCP-1 (2.4+/-0.2 fold). Fractionation of the serum showed that this effect on human tubular epithelial cells was reproduced by a fraction of molecular weight 40-100 kDa. The predominant proteins in this fraction were albumin and transferrin but these purified proteins alone did not alter secretion of PDGF-AB or MCP-1.

CONCLUSION

This data demonstrates that human tubular cells exposed to proteins, which would be filtered in glomerular disease, produce inflammatory mediators with the potential to stimulate inflammation and scarring in the interstitium of the kidney.

Tubular function and tubulointerstitial disease

Tubular transport determined by the fractional excretion (FE) of filtered solutes was studied in 129 nephrotic patients; 72 patients with mesangial proliferation (MesP-NS) and intact tubulointerstitium (group 1), 13 patients with MesP-NS and superimposed tubulointerstitial fibrosis (TIF; group 2), 27 patients with mild focal segmental glomerulosclerosis (FSGS; group 3), and 17 patients with severe FSGS (group 4). In the 72 nephrotic patients with MesP-NS and normal tubulointerstitium (no TIF), tubular transport was intact (FE of sodium [FENa], 0.5 +/- 0.5; FE of calcium [FECa], 0.3 +/- 0.3; FE of phosphate [FEPO4], 14 +/- 13; FE of uric acid [FEUA], 9.8 +/- 5; FE of magnesium [FEMg], 1.3 +/- 0.5). In the 13 nephrotic patients with MesP-NS and superimposed TIF (4.9% +/- 2%), there was no difference in FE solutes from those in group 1 except for FEMg (3.3 +/- 0.9; P < 0.001). In the 27 nephrotic patients with mild FSGS (TIF, 28% +/- 9%), four of five variables of FE solutes (FENa, 1.2 +/- 0.7; P < 0.001; FECa, 0.9 +/- 0.8; P < 0.001; FEPO4, 17 +/- 12; P, not significant; FEUA, 16.5 +/- 8; P < 0.001; FEMg, 4. 1 +/-1; P < 0.001) were significantly different from those of patients with MesP-NS without TIF, and two of five variables (FECa, FEMg) were statistically different from those of patients with MesP-NS with TIF. In the severe category of FSGS (TIF, 69% +/-19%), all FE solutes were statistically different from the other groups (FENa, 4.8 +/- 3; FECa, 2 +/- 1; FEPO4, 47 +/- 24; FEUA, 37 +/- 18; FEMg, 12 +/- 6). Thus, the results imply that (1) normal tubular transport reflects an underlying intact tubulointerstitial structure, whereas tubular dysfunction indicates an underlying tubulointerstitial disease, and (2) FEMg is the most sensitive index to detect an early abnormality of tubular structure and function.

Apical proteins stimulate complement synthesis by cultured human proximal tubular epithelial cells

There is increasing evidence to suggest that the renal tubular epithelium is important in the pathogenesis of progressive renal failure resulting from persistent proteinuria. The role of complement in the progression of chronic renal failure is not well defined. The purpose of this study was to characterize the production of complement by human proximal tubular epithelial cells exposed to serum proteins at the apical surface. Complement C3 gene expression was analyzed by reverse transcription and PCR. C3 protein biosynthesis was confirmed by metabolic labeling followed by immunoprecipitation and quantified by enzyme-linked immunosorbent assay. In the quiescent state, proximal tubular epithelial cells grown on permeable membrane supports secreted C3 predominantly into the apical medium. The addition of 5 mg/ml serum proteins led to an 8.9-fold increase in basolateral C3 secretion and a 2.1-fold increase in apical C3 secretion, altering the ratio of basolateral: apical C3 secretion from 0.44 +/- 0.16 to 1.87 +/- 0.52. C3 mRNA expression was also upregulated in a time- and dose-dependent manner. Serum fractionation demonstrated that the stimulant responsible for these effects was in the molecular weight range 30 to 100 kD. The observed phenomenon was not reproduced when purified human albumin alone was used as the stimulant. These findings could provide a possible mechanism for the link between proteinuria and interstitial fibrosis. This may have potential implications for strategies directed against complement in retarding the progression of chronic renal failure.

Paracrine stimulation of human renal fibroblasts by proximal tubule cells

Paracrine stimulation of human renal fibroblasts by proximal tubule cells.

BACKGROUND

Interstitial fibrosis strongly predicts the degree and progression of renal failure in human renal disorders. Since active fibrosis tends to initially occur in a peritubular distribution, the possibility that human proximal tubule cells (PTC) relay fibrogenic signals to neighboring cortical fibroblasts was examined in vitro.

METHODS

Cell proliferation (cell counts and thymidine incorporation), total collagen synthesis (proline incorporation), matrix metalloproteinase (MMP) activity (gelatin zymography), and autocrine secretion of insulin-like growth factor-I (IGF-I) were measured in primary cultures of human cortical fibroblasts cocultured with PTC or exposed to PTC-conditioned media (PTCCM).

RESULTS

Cell numbers and thymidine incorporation rates were increased in cortical fibroblasts cocultured with PTC (136.4+/-7.3% and 119.3+/-8.2% of control values, respectively, P < 0.05) or incubated in PTC-CM (114.0+/-5.9%, P < 0.05 and 146.7+/-13.3%, P < 0.05, respectively). PTC-CM stimulated cortical fibroblast collagen synthesis (13.5+/-1.0% vs. 10.8+/-0.7%, respectively, N = 24, P < 0.05) and MMP-2 and MMP-9 secretion. Cortical fibroblast secretion of IGF-I binding protein-3 (IGFBP-3), which in turn modulates the autocrine and paracrine actions of IGF-I, was enhanced in the presence of PTC-CM compared with control (1162.2+/-94.2 vs. 969.1+/-58.9 ng/mg protein/day, P < 0.05), but no change was observed in cortical fibroblast secretion of IGFBP-2 (260.9+/-38.8 vs. 290.9+/-36.6 ng/mg protein/day, P = NS) or IGF-I (56.7+/-6.6 vs. 57.0+/-6.8 ng/mg protein/day, P = NS). Human PTC secreted transforming growth factor-beta1 (TGF-beta1) and the AB heterodimer of platelet-derived growth factor (PDGF-AB) in a time-dependent fashion and the augmentation of cortical fibroblasts mitogenesis, collagen synthesis and IGFBP-3 secretion induced by PTC-CM was replicated by exogenous TGF-beta1 and PDGF. Furthermore, the stimulatory effects of PTC on cortical fibroblasts were potentiated in transiently acidified PTC-CM (which activated latent TGF-beta1), and were abrogated by neutralizing antibodies specifically directed against TGF-beta1 and PDGF-AB. Cortical fibroblasts in turn released a soluble factor(s) into cortical fibroblast-conditioned media that reciprocally stimulated PDGF-AB production by PTC (4.79+/-1.55 vs. 0.78+/-.06 ng/mg protein/day, P < 0.05).

CONCLUSIONS

PTC modulate the biological behavior of neighboring cortical fibroblasts in the human kidney through paracrine mechanisms, which include the production and release of PDGF-AB and TGF-beta1. Renal insults that result in proximal tubule injury may perturb this paracrine interaction, thereby culminating in excessive fibroblast proliferation and interstitial fibrosis.

Accelerated fibrosis and collagen deposition develop in the renal interstitium of angiotensin type 2 receptor null mutant mice during ureteral obstruction

We examined the role of angiotensin in renal remodeling that is specifically channeled through the angiotensin type 2 receptor (AT2 receptor). Previously, we observed that in mouse embryonic kidneys the AT2 mRNA is predominantly expressed in the mesenchyme. We therefore chose a model of unilateral ureteral obstruction, characterized by activation of the renin-angiotensin system, while fibrosis develops prominently within the renal interstitium. Male wild-type mice (Agtr2 -/Y) and mice null mutant for the AT2 gene (Agtr2 -/Y) were subjected to a complete unilateral ureteral ligation for 5 or 14 days. Obstructed kidneys of Agtr2 -/Y mice showed more severe interstitial fibrosis than those of Agtr2 +/Y mice, confirmed by increased collagen by point-counting on Masson trichrome stained sections, and increased alpha 1(I) collagen mRNA expression by Northern blot. Immunohistochemistry staining for PCNA (a marker of cell proliferation), F4/80 (a marker of macrophages), vimentin (a marker of fibroblasts), and alpha SMA (a marker of myofibroblasts) revealed that, while the two groups were comparable in the degree of cell proliferation and macrophage infiltration, fibroblasts/ myofibroblasts were present in a greater abundance in obstructed kidneys of Agtr2 -/Y mice than in Agtr2 +/Y at both 5 and 14 days after obstruction. Moreover, cells undergoing apoptosis were significantly less in Agtr2 -/Y than in Agtr2 +/Y. Thus, the AT2 receptor significantly impacts the remodeling process within renal interstitium, potentially by regulating the population of collagen-producing cells.

The importance of tubulointerstitial injury in the early phase of primary glomerular disease

OBJECTIVES

As tubulointerstitial damage is regarded secondary to glomerular injury in primary glomerulopathies, we assessed lesions to renal tubulointerstitium in recently diagnosed primary glomerular diseases and evaluated their impact on progression of the disease during the first 2 years after diagnosis.

DESIGN

A nonrandomized prospective study assessing tubulointerstitial morphometry at diagnosis, markers of tubular function within the next 6 months and progression of the disease (creatinine clearance) during 24 months' follow-up.

SETTING

Single tertiary referral centre.

SUBJECTS

Forty-six patients with primary glomerular disease, the diagnostic oligobiopsy performed within 2 months of the onset of clinical symptoms.

INTERVENTIONS

All patients were subjected to antiinflammatory/immunosuppressive treatment.

MAIN OUTCOME MEASURES

Alterations in results of tubulointerstitial morphometry and tubular function tests, correlations between these variables and parameters of nephrosis/renal function, selection of the most accurate predictor of disease progression within 24 months after diagnostic biopsy.

RESULTS

Function of proximal tubules, markedly deteriorated at the time of diagnosis, significantly improved 6 months later (urinary beta2-microglobulin: P < 0.0025), along with reduction in proteinuria (P < 0.00125). No appreciable alterations in function of distal tubules were noted. Morphometric indices revealing interstitial expansion and tubular atrophy significantly correlated with creatinine clearance at 6 months (P = 0.032) and were the best predictors of deteriorating renal function at 24 months. Excretion of beta2-microglobulin at the time of diagnosis was the best marker for impairment of glomerular filtration 6 months later.

CONCLUSIONS

Significant damage to cortical tubulointerstitium occurs concurrently with glomerular injury in primary glomerulopathies and may predict the clinical course of the disease already in its initial phase.

Chronic hypoxia induces proliferation of cultured mesangial cells: role of calcium and protein kinase C

The effect of hypoxia on the proliferation of cultured rat mesangial cells was examined. To evaluate the underlying signaling mechanisms, the roles of intracellular calcium ([Ca2+]i) and protein kinase C (PKC) were determined. Quiescent cultures were exposed to hypoxia (3% O2) or normoxia (18% O2), and [3H]thymidine incorporation, cell number, [Ca2+]i, and PKC were assessed. Mesangial cells exposed to 28 h of hypoxia exhibited a significant increase in [3H]thymidine incorporation followed by a significant increase in cell number at 72 h in comparison with respective normoxic controls. Hypoxia induced a biphasic activation of PKC, reflected by translocation of the enzyme activity from cytosol to membrane at 1 h, a return to baseline at 4 and 8 h, with subsequent reactivation from 16 to 48 h. In addition, hypoxia-induced proliferation was prevented by a PKC inhibitor 1-(5-isoquinolinylsulfonyl)-2-methylpiperazine (H-7). Cells exposed to hypoxia produced progressive increases in resting [Ca2+]i from 15 to 60 min which remain sustained up to 24 h of examination. Verapamil significantly prevented the hypoxia-induced proliferation, and both verapamil treatment and incubations in a calcium-free medium for 1 h blocked the hypoxia-induced stimulation of [Ca2+]i as well as PKC. These results provide the first in vitro evidence that chronic hypoxia induces proliferation of cultured glomerular mesangial cells, which is mediated by the stimulation of [Ca2+]i and the subsequent activation of PKC.

Characterization of proteinuria in primary glomerulonephritides: urinary polymers of albumin

In 142 patients with primary glomerulonephritis (GN), there were polymers of albumin (PAs) in the urine samples of 87% of 15 minimal-change disease (MCD) patients, 52% of 27 focal segmental glomerulosclerosis (FSGS) patients, 51% of 47 membranous glomerulonephritis (MGN) patients, 55% of 20 membranoproliferative glomerulonephritis (MPGN) patients, and 9% of 33 immunoglobulin A nephropathy (IgAN) patients (P = 0.000). In IgAN, only three patients with nephrotic syndrome were PA positive. The PAs were significantly correlated with nephrotic syndrome (NS) (P = 0.000) and with the degree of proteinuria, ranging from 8% in patients with proteinuria less than 0.5 g/d to 58% in patients with proteinuria > or = 15.0 g/d (P = 0.001), but 40% of the nephrotic syndrome patients were PA-negative despite values of proteinuria comparable to those of PA-positive patients, suggesting that the presence of PAs is not simply related to protein loss, but probably to some other unidentified factor or lesion. For 72 patients (43 with NS) (22 FSGS, 36 MGN, and 14 MPGN patients) with normal renal function at entry (serum creatinine, 1.02 +/- 0.23 mg/dL) and a mean follow-up duration of 52 +/- 27 months, for whom PAs were determined and urinary protein characterized by sodium-dodecyl-sulphate polyacrylamide gel electrophoresis (SDS-PAGE) at the beginning of the follow-up period, the functional outcome was correlated with the patterns of proteinuria. Chronic renal failure (CRF) developed in 24% of all 72 patients, in 36% of the PA-positive patients, in 9% of the PA-negative patients (P = 0.007), in 44% of the SDS-PAGE 10-kd mixed glomerulotubular pattern patients, and in 17% of the SDS-PAGE 23-kd mixed-pattern patients (P = 0.001). The association of PAs with the 10-kd pattern enhanced the predictive value for CRF outcome: CRF developed in 62% of the PA-positive patients with the 10-kd pattern compared with 11% of the PA-negative patients with the 23-kd pattern (P = 0.0001). CRF developed in 32% of 43 patients with the nephrotic syndrome, in 48% of the PA-positive patients, and in 11% of the PA-negative patients (P = 0.037); in 50% of the 10-kd patients and in 24% of the 23-kd patients (P = 0.007); and in 70% of the PA-positive patients with the 10-kd pattern and 14% of the PA-negative patients with the 23-kd pattern (P = 0.001). In a retrospective study of 21 treated patients (11 FSGS, nine MGN, and one MPGN patient), a response to therapy with complete or partial remission was observed in 57% of all 21 patients; in 58% of patients with the nephrotic syndrome; in 88% of the PA-negative patients versus 38% of the PA-positive patients (P = 0.027); in 90% of the 23-kd patients versus 27% of the 10-kd patients (P = 0.004); and in 100% of the PA-negative patients with the 23-kd pattern versus 12% of the PA-positive patients with the 10-kd pattern (P = 0.001). In conclusion, urinary PAs are associated with GN characterized by lesions mainly localized in the glomerular capillary wall, with the presence of the nephrotic syndrome, and with the degree of proteinuria. In patients with FSGS, MGN, MPGN, and normal renal function at entry, the presence of polymers has a predictive value for CRF outcome; this value is enhanced by the contemporaneous presence of an SDS-PAGE proteinuric pattern with low molecular weight proteins up to 10-kd, which is known to be associated with diffuse tubulointerstitial lesions. Therefore, the best predictive value for either CRF outcome or for response to therapy was provided by a combination between a marker associated with the degree of proteinuria and the types of GN characterized by lesions mainly localized in the glomerular capillary wall and a marker associated with tubulointerstitial damage (SDS-PAGE mixed glomerulotubular pattern with low molecular weight proteins between 20 and 10 kd).

Hypoxia stimulates proximal tubular cell matrix production via a TGF-beta1-independent mechanism

Tubulointerstitial fibrosis is characterized by tubular basement membrane thickening and accumulation of interstitial extracellular matrix (ECM). Since chronic low-grade hypoxia has been implicated in the pathogenesis of fibrosis and proximal tubular epithelial cells (PTE) are sensitive to oxygen deprivation, we hypothesized that hypoxia may stimulate ECM accumulation. In human PTE, hypoxia (1% O2, 24 hr) increased total collagen production (15%), decreased MMP-2 activity (55% +/- 13%; control = 100%) and increased tissue inhibitor of metalloproteinase-1 (TIMP-1) protein. Collagen IV mRNA levels decreased while collagen I mRNA increased, suggesting induction of interstitial collagen. Hypoxia-induced changes persisted on re-oxygenation with increased expression of TIMP mRNAs. A potential mediator for these effects is transforming growth factor-beta1 (TGF-beta1), a major pro-fibrogenic factor produced by PTE. Although hypoxia stimulated TGF-beta production (2- to 3-fold), neutralizing anti-TGF-beta1 antibody did not abolish the hypoxia-induced changes in gelatinase activity, TIMP-1, collagen IV or collagen I mRNA expression, implying that TGF-beta1 is not the mediator. Furthermore, exogenous TGF-beta1 (0 to 10 ng/ml) did not mimic hypoxia, as it stimulated MMP-2 activity and increased the expression of collagen IV, collagen I and TIMP-1 mRNA. The data suggest that hypoxia may be an important pro-fibrogenic stimulus independent of TGF-beta1.

Interstitial myofibroblasts: predictors of progression in membranous nephropathy

AIMS

To determine the role of interstitial myofibroblasts in the progression of membranous nephropathy; and to assess the predictive value of quantifying myofibroblasts in determining long term renal outcome.

METHODS

All cases of membranous nephropathy, diagnosed by renal biopsy at University Hospital of South Manchester between 1984 and 1987, were studied retrospectively. The biopsy specimens (n = 26) were reviewed and analysed morphometrically to measure interstitial volume as a proportion of the total volume of renal cortex, and numbers of interstitial myofibroblasts (cells positive for alpha-smooth muscle actin within the interstitium). Clinical data, with a follow up of seven to eight years, was available for 24 patients, and renal outcome was correlated with pathological changes in the initial diagnostic biopsy specimen.

RESULTS

The number of myofibroblasts and interstitial volume were inversely correlated with creatinine clearance at the initial biopsy, and at the end of follow up. Percentage sclerosed glomeruli or stage of glomerular disease, assessed by electron microscopy, did not correlate with renal function at initial biopsy or during follow up. The number of myofibroblasts, but not interstitial volume, correlated with severity of proteinuria at initial biopsy. Of 15 biopsy specimens showing no or mild interstitial fibrosis, four showed a notable increase in the number of interstitial myofibroblasts. All of these patients developed chronic renal failure, compared with three of 11 patients whose specimens showed no or a mild increase in myofibroblast numbers.

CONCLUSIONS

Interstitial myofibroblasts play a role in the development of interstitial fibrosis and progressive renal failure in membranous nephropathy. Increased numbers of myofibroblasts in biopsy specimens showing only mild fibrosis may predict subsequent chronic renal failure.